The second-longest period of declining rates occurred between November 2000 and July 2003, when the annual percentage yield fell about 2.9 percent. Historically, it has taken an average of two years for deposit rates to begin climbing again after a decline cycle, the firm found.

"The length and severity of the current decline cycle in deposit rates is an indication that the last recession was different than previous recessions in the past 20 years," Market Rates Insight executive vice president Dan Geller said.